title: Chiral anion catalysis in the enantioselective 1,4-reduction of the 1-benzopyrylium ion as a reactive intermediate.
abstract: Anionic! Novel chiral anion catalysis of the enantioselective 1,4-reduction of the 1-benzopyrylium ion by a chiral phosphoric acid was accomplished with a Hantzsch ester as the reducing agent. The enantioselective reduction established is composed of a two-step consecutive transformation involving stereoablative loss of the hydroxy group from racemic 2H-chromen-2-ol derivatives to generate the achiral 1-benzopyrylium ion as a reactive key intermediate.
authors.affiliation: Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578 (Japan), Fax: (+81) 22-795-6584; Research and Analytical Center for Giant Molecules, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578 (Japan). mterada@m.tohoku.ac.jp.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Terada
authors.forename: Takuto
authors.initials: T
authors.lastname: Yamanaka
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Toda
keywords: Brønsted acids; asymmetric catalysis; benzopyrylium; enantioselective reduction; organocatalysis